Human eye Emmetropia and Ametropia

• Emmetropia


  The medical term for naturally occurring clear vision. A person with emmetropia does not have any refractive errors. When light enters an emmetropic eye, an image focuses perfectly on the retina.

  
• Ametropia


  The medical term for someone who does not have clear vision. A person with ametropia has refractive errors. When light enters an ametropic eye, it does not focus an image on the retina.

  
• Types of ametropia


  • Hyperopia (farsightedness)
  • Myopia (nearsightedness)
  • Presbyopia
  • Astigmatism
• Hyperopia


  The condition whereby light focuses images behind the retina. People with hyperopia can see objects clearly when they are far away but have difficulty seeing objects when they are near.

  
• Correcting hyperopia


  1. Use a converging lens

  2. The image focuses on the retina

  
• Myopia


  The condition whereby light focuses images in front of the retina. People with myopia can see objects clearly when they are near but have difficulty seeing objects when they are far away or at a distance.

  
• Correcting myopia


  1. Use a diverging lens

  2. The image focuses on the retina

  
• Presbyopia


  Age-related farsightedness, a natural part of the aging process of the eye's lens. It usually begins around age 40, when the lens starts to lose some flexibility, and it affects everyone.

  
• Astigmatism


  Both near and distant objects appear blurry because the cornea is irregularly curved. Astigmatism often accompanies myopia or hyperopia.

  
• Treating astigmatism


  Eyeglasses or contacts

  
• Emmetropic eyes


  • Do not require corrective lenses, but are still susceptible to conditions unrelated to visual acuity
  • The best way to promote healthy vision is through proper care and preventative measures, from basic eye protection to routine eye exams

  
• UV protection


  UV rays can be harmful to the eyes, regardless of vision clarity. Too much exposure to sunlight can increase your risk of sunburned eyes, cataracts, snow blindness, eye cancer and growths in or near the eye.
• Be sure to protect your eyes from the brightness of the sun with 100% UV or UV400 protection in your sunglasses.
• Additional eye protection


  If you work outdoors or participate in sports or other activities that could potentially harm your eyes, it is important to know what kind of protective eyewear you need. Sports glasses or safety goggles, in addition to UV protection, are key in preventing eye injuries that could complicate vision.
• Some people who spend a great deal of time looking at computers find that blue light glasses are beneficial for keeping them comfortable while working on their devices.
• Routine eye exams


  Regardless of the natural sharpness of your vision, certain conditions can develop with age or due to your family's medical history. Annual comprehensive eye exams are the best way to detect any abnormalities or changes in vision. The earlier a problem is detected, the sooner it can be corrected.

  
• Hyperopia is farsightedness, where the image falls behind the retina.
• Myopia is nearsightedness, where the image falls short of the retina.
• Astigmatism occurs when there are irregularities on the surface of the cornea or lens that cause light rays to focus at different points instead of one point.